If you're abroad and hear someone speaking your native language there
is an excellent chance you will talk to them. Strange, you don’t
introduce yourself to many strangers on the train back home.

The context changes everything, even in your community.

People in an elevator work tirelessly to avoid eye-contact. Until it breaks. Then they're going through an experience together.

Did you become friends with your college buddies because you liked them or because you were in a context that gave you shared experiences, common purposes, insiders, outsiders etc..?

You can plan the context. You can make people feel they are in an experience together. You need insiders, outsiders, boundaries, common purpose, shared experiences. Plan these in advance. You can't force people to become friends, but you can make it difficult for them not to become friends.

Plan the context in advance. What are the shared experiences your community will go through? What seperates insiders from outsiders (beyond registration). What is the common purpose? Why do people need to talk for that purpose?